1. Field of the Invention
The present invention generally relates to devices for measuring dimensions of a body. More particularly, this invention relates to devices for measuring the profile and/or diameter of a cylindrical body, such as a roll used in the production of sheet products.
2. Description of the Related Art
Cylindrical rolls used to roll sheet products, such as aluminum and paper, are required to have a particular profile in order to obtain a flat rolled product. For this reason, the contours or profiles of such rolls must be accurately measured and variations in diameters along their lengths recorded. Freestanding saddle-type micrometers have been widely used for this purpose.
As represented in U.S. Pat. No. 5,088,207 to Betsill et al., a freestanding saddle micrometer generally includes a saddle supported on wheels for rolling (xe2x80x9cskatingxe2x80x9d) along the longitudinal length of a roll. As used herein, the term xe2x80x9cfreestandingxe2x80x9d is used in reference to a saddle-type micrometer in that such micrometers are not mounted to a grinder or other permanent apparatus, but instead are portable and placed on the roll being evaluated. The Betsill et al. saddle micrometer is a caliper-type unit, in that the micrometer has oppositely-disposed arms that extend outward and downward from the saddle so as to be located on opposite sides of a roll when the micrometer is placed on top of a roll. The arms are supported by a rocking crossbar. One of the arms supports a counterweight or follower probe, while the second arm carries an indicator probe, such as a dial indicator or an LVDT (linear variable differential transducer). By locating the follower and indicator probes on their respective arms to be diametrically opposite each other relative to the roll, variations in the diameter of the roll can be detected by skating the saddle along the length of the roll. If a dial indicator is used as the indicator probe, the saddle must make stops along the length of the roll to allow manual recording of the dial indicator reading. If an LVDT or other electronic transducer is used, variations in the roll diameter can be continuously recorded electronically. The saddle is preferably equipped with an encoder to measure the distance skated along the length of the roll, and a minicomputer is mounted on the frame to read, record, and present input data from the LVDT and the encoder.
Existing saddle micrometers have several shortcomings that involve compromises in weight, rigidity, balance and operation. In terms of weight and rigidity, existing saddle micrometers have taken two approaches: either ignore weight for the sake of rigidity, which results in a unit that operators find difficult to handle but will, provide accurate readings; or reduce weight to provide a unit that can be more easily handled, sacrificing rigidity to the extent that imprecise readings may occur. This problem is exacerbated if electronic probes are used, since the unit is constantly in motion as readings are taken. Nonetheless, lighter-weight units have generally been more widely accepted because of the difficulty in handling the heavier, more rigid units. Existing saddle micrometers are also generally top heavy, with the result that the units are more prone to slip off the top of a roll. In the event of slipping off a roll, if a heavier unit is used the unit will probably not be damaged but the operator is at risk of injury. On the other hand, if a lightweight unit slides off a roll, the unit is much more likely to be damaged.
Finally, from an operational standpoint, existing caliper-type micrometers do not actually measure roll diameter, but instead are limited to determining the profile of a roll, i.e., variations in diameter along the length of a roll. Furthermore, micrometers have relied on an onboard minicomputer to acquire and process the collected data. Because of the limited computing power of these minicomputers, many electronic saddle micrometers are a simple unit that is easy to learn and operate, but provides only basic profile information. More advanced units are available that require extensive training to learn and skill to operate. While providing more detailed profile information, roll history and hard copy printout, in practice such enhanced capabilities were rarely used because of the difficulty in learning how to operate the onboard minicomputer.
From the above, it can be seen that it would be desirable if a saddle micrometer were available that overcame the shortcomings of the prior art, including improved rigidity, balance and operational features without incurring excessive weight.
The present invention provides a freestanding micrometer and method for determining the diameter of a cylindrical body. The micrometer and method can be adapted to measure variations in diameter along a longitudinal length of a cylindrical body, such as a roll used in the production of metal and paper sheet products. The micrometer comprises a housing and means for supporting the housing on a surface of the cylindrical body while the cylindrical body is oriented so that its longitudinal axis is approximately horizontal. A first measurement means is movably supported by the housing so that the position of the first measurement means can be altered in a lateral direction that is approximately perpendicular to the longitudinal axis of the cylindrical body. The first measurement means is adapted for sensing a first surface point of the cylindrical body laterally spaced apart from the housing and disposed in a cross-sectional plane of the cylindrical body. The micrometer further comprises a second measurement means mounted to the housing for contact with a second surface point of the cylindrical body disposed in the cross-sectional plane of the cylindrical body. The first surface point defines a terminal of a chord lying in the cross-section plane of the cylindrical body, while the second surface point defines a location along the length of the chord. Finally, the micrometer is equipped with means for determining the diameter of the cylindrical body based on the length and height of the chord ascertained from first and second outputs of the first and second measurement means, respectively.
The freestanding micrometer described above makes possible a method of determining the diameter of a cylindrical body without diametrically-opposed sensing probes. According to the method, the housing is placed on the surface of the cylindrical body while the cylindrical body is oriented so that its longitudinal axis is approximately horizontal. The first measurement means is then positioned relative to the housing in a lateral direction approximately perpendicular to the longitudinal axis of the cylindrical body, and produces a first output signal by sensing a first surface point of the cylindrical body laterally spaced apart from the housing and disposed in a cross-sectional plane of the cylindrical body. A second output signal is produced with the second measurement means by sensing a second surface point of the cylindrical body adjacent the housing and disposed in the same cross-sectional plane of the cylindrical body as the first surface point. As such, the first and second surface points sensed by the first and second measurement means define, respectively, a chord terminal and a point along the length of the chord, and the diameter of the cylindrical body is determined based on the length and height of the chord ascertained from the first and second output signals.
In view of the above, it can be seen that the freestanding micrometer of this invention structurally differs from freestanding caliper-type saddle micrometers of the prior art by its capability to determine the diameter of a cylindrical body, instead of just the profile of the body. Furthermore, the micrometer is able to make use of a first sensing element spaced apart from the housing by a single arm, and a second sensing element carried close to or on the housing. Because of its compact construction, the micrometer of this invention can be constructed to be relatively lightweight, resulting in a unit that is easier and safer to use. In addition, the micrometer of this invention can be constructed to be rigid relative to its weight, resulting in more reliable and precise data acquisition.
Other objects and advantages of this invention will be better appreciated from the following detailed description.